While cheek swabs are a more child-friendly alternative, the amount of DNA that is retrieved is very low, compared to that obtained from blood samples.

In addition, when researchers investigate the genetics of diseases with a low prevalence it takes time to find and collect the number of samples they need.

This means they need samples that can be easily stored for long periods of time.

Saliva study

Previous research has suggested that saliva samples might yield similar levels of DNA to blood.

It's certainly a more child-friendly method of collecting DNA, but how convenient is it to store it for long periods of time?

To investigate this question, Anthonappa and colleagues collected blood samples from 10 participants and salvia from 50 participants.

They extracted DNA immediately, and then at different time periods after various storage conditions.

The researchers found that saliva was easier to store than blood, and yet provided comparable amounts of DNA useful for research.

While blood must be kept cold and DNA must be extracted from it within 24 hours, saliva could be stored at 37°C for 18 months without any loss of useful DNA.

"It doesn't affect its quality and you can still use it for genotyping," says Anthonappa.

Extra teeth

Anthonappa and colleagues started looking into the potential of saliva as a source of DNA while researching the genetic markers of a rare dental condition in which children grow more teeth than normal.

The condition is often not picked up until children are 7 or 8, by which time removal of the extra teeth can cause problems.

Once identified, genetic markers for the condition could be used to narrow down children at risk for the condition, says Anthonappa, adding these children could be x-rayed and treated early if required.